1. Field of the Invention
The present invention relates to a process for obtaining a 1,3-butadiene homopolymer in the presence of one or more monoolefin(s) with 4 carbon atoms, for example from a steam-cracked C4 naphtha fraction, said homopolymer exhibiting microstructural and macrostructural properties making it suitable for use in tire treads.
2. Description of Related Art
Steam-cracked C4 naphtha fractions essentially contain 1,3-butadiene in a mass fraction of typically between 20 and 50% and monoolefins comprising 1-butene, 2-butene and isobutene in a mass fraction of between 70 and 40%.
Depending on whether the naphtha steam cracking is of the “low severity” type (i.e. performed at a temperature of less than 800° C. with a dwell time of the order of one second) or alternatively of the “high severity” type (i.e. performed at a temperature of almost 900° C. with a dwell time of the order of half a second), a C4 fraction is obtained which has a mass fraction of 1,3-butadiene which is respectively lower or higher in proportion to the mass fraction of the monoolefins.
With the aim of performing selective polymerization of 1,3-butadiene with elevated activity starting from a steam-cracked C4 naphtha fraction, the 1,3-butadiene content of said fraction is enriched such that the 1,3-butadiene is present in the enriched fraction in a mass fraction of close to 100%. It has in fact been found that the above-stated monoolefins impair the yield of the 1,3-butadiene polymerization reaction.
This enrichment of the C4 fraction has the drawback of requiring the performance of a complex separation process and, consequently, of entailing relatively high operating costs for homopolymerization of the 1,3-butadiene.
This is why it has in the past been attempted to perform selective polymerization of the 1,3-butadiene from an unenriched C4 fraction, i.e. containing 1,3-butadiene in a mass fraction of less than or equal to 50%.
U.S. patent specification U.S. Pat. No. 3,066,128 presents a process for the selective polymerization of butadiene starting from a steam-cracked C4 naphtha fraction, which consists in using a catalytic system based cobalt or nickel halide and an activating agent for example consisting of an alkylaluminum or an alkylaluminum chloride.
French patent specification FR-A-2,496,673 presents another process for the selective polymerization of butadiene starting from a steam-cracked C4 naphtha fraction, which consists in using a catalytic system based on a lithiated initiator.
One major drawback of these selective polymerization processes resides in the reduced polymerization yields in the presence of monoolefins which these catalytic systems bring about.